I just would like to create a topic for a project released on GitHub on November 2016 called UUV Simulator, mainly aimed to simulate unmanned underwater vehicles such as AUVs and ROVs. It includes Gazebo plugins and several ROS nodes and it is built modularly to help the construction of complex simulation environments for underwater vehicles.
The project has been going through a lot of updates and changes thanks to several suggestions from the community and it has grown significantly since we managed to publish it on GitHub.
Recently I added an improved documentation site (still being updated) and some extra packages for robot models and some useful ROS nodes, such as a plume simulation, that are also available here https://github.com/uuvsimulator.
Any suggestions or criticisms are very welcome.